JP6523202B2 - Alignment method of local light input / output optical system and local light input / output optical device - Google Patents

Description

  The present disclosure relates to technology for inputting and outputting light from the side of an optical fiber.

  In the local light input / output optical system, if the light reception coupling efficiency is low, an expensive high amplification factor amplifier must be used to compensate. Therefore, in order to improve the light reception coupling efficiency, it has been proposed to use a double clad fiber (dual mode fiber) having both a single mode core and a multi mode core as a probe fiber, instead of the conventional single mode fiber See, for example, non-patent documents 1, 2 and 3. ]. This is because the larger the core diameter of the fiber used for the probe, the higher the light reception coupling efficiency.

  In this specification, a double clad fiber may be abbreviated as "DCF" and a single mode fiber may be abbreviated as "SMF". Also, "single mode fiber" means an optical fiber that propagates only in the fundamental mode at the wavelength of the propagating light, and "multimode fiber" means an optical fiber that can propagate in multiple modes at the wavelength of the propagating light.

  FIG. 1 is a view for explaining the structure of a double clad fiber. It consists of a Ge-doped single mode core, an undoped multimode core, and an F-doped cladding. When a single mode fiber is connected, it operates as a single mode fiber, and when a multi mode fiber is connected, it operates as a multi mode fiber.

  FIG. 2 is a diagram for explaining the state of local light input / output by the double clad fiber. The double clad fiber 11 receives the light (leakage light) output from the bent portion of the main optical fiber 1 by the multimode core (FIG. 2 (A)). For this reason, if the double clad fiber is used, the light reception intensity can be increased as compared with the light reception by the single mode fiber, and therefore, a low cost ordinary amplifier can be used. On the other hand, the double clad fiber 11 makes light enter the bent portion of the main optical fiber 1 via the single mode core (FIG. 2 (B)). For this reason, if a double clad fiber is used, the beam diameter can be made smaller compared to the incidence of the multimode fiber, and the incidence coupling efficiency with the main optical fiber 1 can be enhanced.

  FIG. 3 is a view for explaining an optical fiber side input / output device 300 using a double clad fiber. The optical fiber side input / output device 300 includes a local light input / output unit 32 having a probe fiber 31 for local light input / output and a relay amplifier 33. The WDM coupler 34 separates the light into an incident wavelength and a light reception wavelength according to the difference between the wavelengths propagating through the single mode core and the multimode core. The incident light is connected from the duplex SFP (Small Form-factor Pluggable) optical transceiver 35 to the SMF 37, the WDM coupler 34, and the probe fiber 31 for local light input / output via the single mode core of the DCF 11 for local light input / output The light received by the probe fiber 31 reaches the duplex SFP optical transceiver 35 via the multimode core of the DCF 11, the WDM coupler 34, and the multimode core of the DCF 38, and the duplex SFP optical transceiver 35 performs transmission and reception. After OE / EO conversion, the station side communicates with the bi-directional SFP optical transceiver 36.

  Tape fibers are widely used as overhead or underground cables in domestic access facilities. Consider applying local light input / output optics to a tape fiber. FIG. 4 is a diagram illustrating a typical tape fiber. The tape fiber is formed of four or eight single-mode fibers covered with a UV curable resin having a diameter of 0.25 mm and further molded into a tape shape by resin coating.

  FIG. 5 is a view for explaining the state of light leaking from the tape fiber. 5 (A) is a perspective view, and FIG. 5 (B) is a side view. Here, since the thickness of the resin varies in units of several tens of μm, the core intervals of the individual optical fibers are also dispersed in several tens of μm and are indefinite. On the other hand, since the core diameter of the optical fiber is about 9 μm, the optical axis alignment to the optimum position between the optical fiber cores needs accuracy of several μm. Since the core position of the optical fiber tape varies in the order of several tens of μm, the side light input / output optical system for the tape fiber needs optical axis alignment to the optimum position every time the target tape fiber is replaced. . In this optical axis alignment, the light reception intensity of light emitted from the bent main optical fiber is used as an index. In the case of using a probe using a single mode fiber, it is possible to finely align the optimum position of the probe with an accuracy of several μm by searching for a position that is the maximum position using the received light intensity as an index.

Kiyokura et al., "Study on improvement of light receiving efficiency of local light input / output technology by using dual mode fiber probe", 2015 Shinkai Communications Society Conference b-13-014 Tanobe et al., "SM / MM dual mode optical fiber", OCS 2007-37 (2007-8) Internet “Solab double clad fiber DCF 13”, https: // www. thorlabs. co. jp / thorcat / TTN / DCF13-SpecSheet. pdf (searched April 1, 2016) Shibata et al., "Study of Optical Line Switching Device Using Side-Side Input-Output Technology", OFT 2013-50 (2014-1) Internet "Light switch", http: // www. diconfiberoptics. com / products / scd 0227 / 0227a. pdf (searched April 1, 2016)

  FIG. 6 shows the result of measurement of the received light intensity with respect to the tip position of the probe fiber for local light input / output (position tolerance curve). The local light input / output optical system using a double clad fiber (dual mode fiber) for the probe expands the width of the position tolerance curve to about the multimode core diameter compared to the one using a conventional single mode fiber, and peaks The intensity change in the vicinity also becomes smooth.

  When alignment is performed via a double clad fiber using light emitted from the bent portion of the main optical fiber as an index, the width of the position tolerance curve is wide, so the received light intensity easily increases with coarse alignment, but the intensity change near the peak Since it is smooth, it becomes difficult to make fine adjustments on the order of several .mu.m necessary for incidence. If the probe can not be adjusted to a position suitable for incidence, even if the light reception coupling efficiency is sufficient, the incidence coupling efficiency is insufficient, transmission can not be performed only by reception, and bidirectional communication may not be established. As described above, an optical fiber side input / output device using a double clad fiber as a probe has a problem that accurate probe alignment is difficult.

  Then, this invention aims at providing the optical fiber side direction input-output apparatus and the probe position alignment method which alignment of the probe of a double clad fiber is easy in order to solve the said subject.

  An optical fiber side input / output device according to the present invention is provided with a dedicated single mode fiber used at the time of alignment.

Specifically, an optical fiber side input / output device according to the present invention is an optical fiber side input / output device that inputs / outputs light to / from a main optical fiber in which a bending portion is formed via the bending portion. ,
A double clad fiber having a single mode core and a multi mode core, one end of which is close to the bend, and the incident light is made incident from the single mode core of the cross section of the one end to the bend and leaked from the bend A probe fiber for receiving light by a single mode core and a multi mode core of the cross section of the one end;
A dedicated single mode fiber that can be connected to the other end of the probe fiber and propagates the leaked light propagated in the single mode core of the probe fiber;
A light receiving device for receiving the leaked light received by the probe fiber from the probe fiber directly or through the dedicated single mode fiber, and measuring the light intensity of the leaked light;
An alignment mechanism for adjusting the position of the one end of the probe fiber;
A control circuit that causes the aligning mechanism to adjust the position of the one end of the probe fiber based on the light intensity of the leaked light measured by the light receiving device;
Equipped with

In particular, the control circuit
The position of the one end of the probe fiber is moved with respect to the alignment mechanism, the light intensity of the leaked light not measured through the dedicated single mode fiber is measured, and the leaked light with respect to the position of the one end of the probe fiber Acquire the first variation curve of the light intensity of
Moving the one end of the probe fiber to a first position centered on the full width at half maximum of the first variation curve with respect to the alignment mechanism;
The position of the one end of the probe fiber is moved in the vicinity of the first position with respect to the alignment mechanism, and the light intensity of the leaked light through the dedicated single mode fiber is measured to obtain the probe fiber Acquiring a second variation curve of the light intensity of the leaked light with respect to the position of one end,
The one end of the probe fiber is moved to a second position at which the second fluctuation curve peaks with respect to the alignment mechanism.

That is, the probe position alignment method according to the present invention is the probe position alignment method of the optical fiber side input / output device,
The first variation of the light intensity of the leaked light relative to the position of the one end of the probe fiber by moving the position of the one end of the probe fiber and measuring the light intensity of the leaked light not passing through the dedicated single mode fiber A rough alignment step of acquiring a curve and moving the one end of the probe fiber to a first position at the center of the full width at half maximum of the first variation curve;
The position of the one end of the probe fiber is moved in the vicinity of the first position, the light intensity of the leaked light through the dedicated single mode fiber is measured, and the leaked light relative to the position of the one end of the probe fiber A fine adjustment step of acquiring a second variation curve of light intensity and moving the one end of the probe fiber to a second position at which the second variation curve peaks with respect to the alignment mechanism;
It is characterized by doing.

  When a single mode fiber is connected to the double clad fiber, the propagation light of the multimode core is removed and only the single mode core propagation light is obtained. When performing coarse alignment, connect the double clad fiber to the light receiving device and perform alignment with the strong light propagating through the multimode core. In the rough alignment, since the peak of the position tolerance curve is flat, the left and right shoulders of the peak at which the light intensity decreases are detected, and the center position thereof is set as the center position of the subsequent fine alignment.

  Thereafter, a dedicated single mode fiber is inserted between the double clad fiber and the light receiving device and fine alignment is performed to determine and maintain an optimum position. Thereafter, the single mode fiber inserted is removed and the double clad fiber is directly connected to the light receiving device to start bi-directional communication.

  Therefore, the present invention can provide an optical fiber side input / output device and a probe position alignment method that facilitates alignment of a double clad fiber probe.

  Further, the control circuit may further move the one end of the probe fiber to a third position spaced apart from the second position by a predetermined distance with respect to the alignment mechanism.

  When the incident wavelength and the light receiving wavelength are different, the optimum position at the incident wavelength may be different from the optimum position at the light receiving wavelength. Therefore, in the above alignment, the relative positional relationship between the optimum position at the incident wavelength and the optimum position at the light receiving wavelength is acquired in advance, and after finely aligning with a dedicated single mode fiber, the probe is moved by the relative position.

  By shifting the probe to the optimal position for incidence, the incidence coupling efficiency can be maximized. On the other hand, when the probe is displaced, it is separated from the light reception optimum position, but since light reception is performed with a multimode core having a wide position tolerance, a value close to the optimum value can be obtained for the light reception coupling efficiency. The present optical fiber side input / output device can maintain high coupling efficiency for both transmission and reception even if the incident wavelength and the light reception wavelength are different.

  The optical fiber side input / output device according to the present invention may have the following form.

An optical fiber side input / output device according to the present invention is an optical fiber side input / output device that inputs / outputs light to / from a main optical fiber in which a bending portion is formed via the bending portion,
A double clad fiber having a single mode core and a multi mode core, one end of which is close to the bend, and the incident light is made incident from the single mode core of the cross section of the one end to the bend and leaked from the bend A probe fiber for receiving light by a single mode core and a multi mode core of the cross section of the one end;
An optical switch for coupling the leaked light propagated by the probe fiber to a dedicated double clad fiber or a dedicated single mode fiber;
A light receiving device for double clad fiber which receives the leaked light propagated by the dedicated double clad fiber connected to the optical switch and measures the light intensity of the leaked light;
A light receiving device for a single mode fiber that receives the leaked light propagated by the dedicated single mode fiber connected to the optical switch and measures the light intensity of the leaked light;
An alignment mechanism for adjusting the position of the one end of the probe fiber;
A control circuit that causes the alignment mechanism to adjust the position of the one end of the probe fiber based on the light intensity of the leaked light measured by the double clad fiber light receiving device or the single mode fiber light receiving device;
Equipped with

An optical fiber side input / output device according to the present invention is an optical fiber side input / output device that inputs / outputs light to / from a main optical fiber in which a bending portion is formed via the bending portion,
A double clad fiber having a single mode core and a multi mode core, one end of which is close to the bend, and the incident light is made incident from the single mode core of the cross section of the one end to the bend and leaked from the bend A probe fiber for receiving light by a single mode core and a multi mode core of the cross section of the one end;
A dedicated single mode fiber which can be connected at one end to the other end of the probe fiber and which propagates the leaked light propagated in a single mode core of the probe fiber;
A connector capable of connecting the other end of the probe fiber or the other end of the dedicated single mode fiber;
A duplex type optical transceiver that receives the leaked light coupled to the connector by a photodiode and outputs the light intensity of the leaked light;
An alignment mechanism for adjusting the position of the one end of the probe fiber;
A control circuit that causes the alignment mechanism to adjust the position of the one end of the probe fiber based on the light intensity of the leaked light output from the duplex optical transceiver;
Equipped with

An optical fiber side input / output device according to the present invention is an optical fiber side input / output device that inputs / outputs light to / from a main optical fiber in which a bending portion is formed via the bending portion,
A double clad fiber having a single mode core and a multi mode core, one end of which is close to the bend, and the incident light is made incident from the single mode core of the cross section of the one end to the bend and leaked from the bend A probe fiber for receiving light by a single mode core and a multi mode core of the cross section of the one end;
An optical switch for coupling the leaked light propagated by the probe fiber to a relay path of a double clad fiber or a dedicated single mode fiber;
A duplex type optical transceiver which receives the leaked light propagated in the relay path of the double clad fiber or the dedicated single mode fiber by a photodiode and outputs the light intensity of the leaked light;
An alignment mechanism for adjusting the position of the one end of the probe fiber;
A control circuit that causes the alignment mechanism to adjust the position of the one end of the probe fiber based on the light intensity of the leaked light output from the duplex optical transceiver;
Equipped with

An optical fiber side input / output device according to the present invention is an optical fiber side input / output device that inputs / outputs light to / from a main optical fiber in which a bending portion is formed via the bending portion,
A double clad fiber having a single mode core and a multi mode core, one end of which is close to the bend, and the incident light is made incident from the single mode core of the cross section of the one end to the bend and leaked from the bend A probe fiber for receiving light by a single mode core and a multi mode core of the cross section of the one end;
An optical switch for coupling the leaked light propagated by the probe fiber to a relay path of a double clad fiber or a dedicated single mode fiber;
A duplex type optical transceiver that receives the leaked light propagated in the relay path of the double clad fiber with a photodiode and outputs the light intensity of the leaked light;
A light receiving device which receives the leaked light propagated by the dedicated single mode fiber and measures the light intensity of the leaked light;
An alignment mechanism for adjusting the position of the one end of the probe fiber;
A control circuit that causes the aligning mechanism to adjust the position of the one end of the probe fiber based on the light intensity of the leaked light output from the duplex optical transceiver or the light intensity of the leaked light measured by the light receiving device;
Equipped with

  The present invention can provide an optical fiber side input / output device and a probe position alignment method in which alignment of a double clad fiber probe is easy.

It is a figure explaining the structure of a double clad fiber. It is a figure explaining the mode of the local light input / output by a double clad fiber. It is a figure explaining the optical fiber side input-output device relevant to the present invention. It is a figure explaining a typical tape fiber. It is a figure explaining the mode of the light which leaks from a tape fiber. (A) is a perspective view, (B) is a side view. It is a result (position tolerance curve) which measured the light reception light intensity to the tip position of a probe fiber. It is a figure explaining the optical fiber side way input-output device concerning the present invention. Connect DCF to PD, receive light via DCF, roughly align, and hold after estimation of peak center position. It is a figure explaining the optical fiber side way input-output device concerning the present invention. Incorporate dedicated SMF, fine alignment via SMF, and hold after determining probe optimum position. It is a figure explaining the optical fiber side way input-output device concerning the present invention. Holds the optimum probe position, removes the dedicated SMF, and switches DCF from PD to WDM coupler. It is a figure explaining the optical fiber side way input-output device concerning the present invention. Bidirectional communication starts via the WDM coupler and the SFP while maintaining the probe optimum position. It is a figure explaining the position tolerance curve of a double clad fiber. It is a figure explaining that the optimal position of a probe fiber changes with differences in wavelength. It is a figure explaining the optical fiber side way input-output device concerning the present invention. Connect SW to PD for DCF, receive light via DCF, roughly align, and hold after estimation of peak center position. It is a figure explaining the optical fiber side way input-output device concerning the present invention. Connect SW to PD for SMF, receive light via SMF, hold roughly after rough alignment and peak center estimation position determination. It is a figure explaining the optical fiber side way input-output device concerning the present invention. Bidirectional communication starts via the WDM coupler and the SFP while maintaining the probe optimum position. It is a figure explaining the optical fiber side way input-output device concerning the present invention. The DCF is connected to the duplex SFP via the WDM coupler, and light reception via the DCF is performed after coarse alignment and peak center estimation position determination. It is a figure explaining the optical fiber side way input-output device concerning the present invention. Incorporate dedicated SMF, fine alignment via SMF, and hold after determining probe optimum position. It is a figure explaining the optical fiber side way input-output device concerning the present invention. Remove the dedicated SMF while holding the probe optimum position. It is a figure explaining the optical fiber side way input-output device concerning the present invention. Connect DCF to WDM coupler. Bidirectional communication starts via the WDM coupler and duplex SFP. It is a figure explaining the optical fiber side way input-output device concerning the present invention. The SW is set to be incident on the duplex SFP via the DCF, received light via the DCF, and roughly aligned and held after the peak center estimation position is determined. It is a figure explaining the optical fiber side way input-output device concerning the present invention. Set SW via SMF, fine alignment via SMF, hold after determining probe optimum position. It is a figure explaining the optical fiber side way input-output device concerning the present invention. Set SW to be incident to SFP via DCF, and start bi-directional communication via duplex SFP. It is a figure explaining the optical fiber side way input-output device concerning the present invention. The SW is set to be incident on the duplex SFP via the DCF, received light via the DCF, and roughly aligned and held after the peak center estimation position is determined. It is a figure explaining the optical fiber side way input-output device concerning the present invention. Set SW via SMF, fine alignment via SMF, hold after determining probe optimum position. It is a figure explaining the optical fiber side way input-output device concerning the present invention. Set SW to be incident to SFP via DCF, and start bi-directional communication via duplex SFP.

  Embodiments of the invention will be described with reference to the accompanying drawings. The embodiments described below are embodiments of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, components having the same reference numerals denote the same components.

(Embodiment 1)
7 to 10 are diagrams for explaining an optical fiber side input / output device 301 of this embodiment. The optical fiber side input / output device 301 is an optical fiber side input / output device that inputs / outputs light to / from the main optical fiber 1 in which the bending portion is formed via the bending portion,
A double-clad fiber 11 having a single mode core and a multimode core, one end of which is close to the bent portion, and incident light is incident on the bent portion from the single mode core of the cross section of the one end and leaks from the bent portion A probe fiber 31 for receiving leaked light by the single mode core and the multi mode core of the cross section of the one end;
A dedicated single mode fiber 19 that can be connected to the other end of the probe fiber 31 and propagates the leaked light propagated in the single mode core of the probe fiber 31;
A light receiving device 15 which receives the leaked light received by the probe fiber 31 directly from the probe fiber 31 or through a dedicated single mode fiber 19 and measures the light intensity of the leaked light;
An alignment mechanism 12 for adjusting the position of the one end of the probe fiber 31;
A control circuit 17 which causes the aligning mechanism 12 to adjust the position of the one end of the probe fiber 31 based on the light intensity of the leaked light measured by the light receiving device 15;
Equipped with
The optical fiber side input / output device 301 further includes a repeater amplifier 33 having a WDM coupler 34, a duplex SFP optical transceiver 35, a bi-directional SFP optical transceiver 36, an SMF 37, and a DCF 38. The probe fiber 31 and the alignment mechanism 12 are provided in the local light input / output unit 32. The light receiving device 15 and the control circuit 17 may be in the relay amplifier 33.

  Although the probe fiber 31 is fixed in the example shown in FIG. 3, in the present embodiment, the probe fiber 31 is mounted on the aligning mechanism 12, and the position is controlled by the control circuit 17. Further, a high sensitivity photodiode (PD) as the light receiving device 15 is connected to the control circuit 17. Since this PD is for position search, may be of high sensitivity, and is not for communication, it is possible to use a slow and inexpensive one.

  The control circuit 17 uses the light intensity received by the light receiving device 15 as an index to issue an instruction to the aligning mechanism 12 so that the tip of the probe fiber 31 is at the optimum position, thereby performing coarse alignment and fine alignment. The procedure is shown below.

The control circuit 17
The position of the one end of the probe fiber 31 is moved with respect to the alignment mechanism 12, and the light intensity of the leaked light not measured through the dedicated single mode fiber 19 is measured. Acquire the first variation curve of the light intensity of
Moving the one end of the probe fiber 31 to a first position at the center of the full width at half maximum of the first variation curve with respect to the alignment mechanism 12;
The position of the one end of the probe fiber 31 is moved relative to the alignment mechanism 12 in the vicinity of the first position, and the light intensity of the leaked light through the dedicated single mode fiber 19 is measured. Acquiring a second variation curve of the light intensity of the leaked light with respect to the position of one end,
The one end of the probe fiber 31 is moved to a second position at which the second fluctuation curve peaks with respect to the alignment mechanism 12.

(Procedure 1: FIG. 7) The DCF 11 connected to the probe fiber 31 is connected to the light receiving device 15. Rough adjustment is performed by the control circuit 17 and the alignment mechanism 12 using the light intensity (first variation curve) received via the DCF 11 as an index. Specifically, the control circuit 17 estimates a peak center from the first variation curve, moves the probe fiber 31 to the position, and holds the probe fiber 31 at the position.

(Procedure 2: FIG. 8) A dedicated SMF 19 is inserted between the DCF 11 and the light receiving device 15, and fine alignment is performed by the control circuit 17 and the alignment mechanism 12 using the light intensity (second variation curve) received via the dedicated SMF 19 as an index. I do. Specifically, the control circuit 17 detects the peak center from the second fluctuation curve, moves the probe fiber 31 to the position, and holds the probe fiber 31 at the position. The dedicated SMF 19 may be installed on the surface of the relay amplifier 33 in advance. The relationship between the first variation curve and the second variation curve will be described later.

(Procedure 3: FIG. 9) While maintaining the optimum position of the probe fiber 31 found in the procedure 2, the dedicated SMF 19 inserted is removed, and the DCF 11 is reconnected to the WDM coupler 34.

(Step 4: FIG. 10) Two-way communication is started while maintaining the optimum position of the probe fiber 31. Specifically, the leaked light from the main optical fiber 1 passes through the single mode core and the multimode core of the probe fiber 31 and the DCF 11, is input to the DCF 38 by the WDM coupler 34, and is O / E converted by the duplex SFP optical transceiver 35. Be done. Then, the O / E converted electrical signal is E / O converted by the bi-directional SFP optical transceiver 36 and transmitted to the station side. On the other hand, the signal from the station side is O / E converted by the bi-directional SFP optical transceiver 36 and E / O converted by the duplex SFP optical transceiver 35. The E / O converted optical signal passes through the SMF 37 and is coupled to the DCF 11 by the WDM coupler 34. Then, this optical signal is emitted from the single mode core of the probe fiber 31 and input to the main optical fiber 1.

  As described above, in this probe position alignment method, coarse alignment is performed using the intensity of the first variation curve of the light intensity acquired using light from the multimode core of DCF 11 as an index, and then via the single mode core via dedicated SMF 19 The second variation curve intensity of the light intensity acquired by using the light of the above is finely aligned as an index. For this reason, it is possible to perform bidirectional communication with both the incident light to the main optical fiber 1 and the leaked light from the main optical fiber 1 with the coupling efficiency increased.

Second Embodiment
In this embodiment, details of the probe position alignment method of the optical fiber side input / output device 301 described in the first embodiment will be described. FIG. 11 is a diagram for explaining the first variation curve and the second variation curve.

  The light intensity of the leaked light of wavelength 1310 nm emitted from the bent portion of the main optical fiber 1 is aligned with the index. Since the reception of leaked light is performed by the multimode core (including a single mode core) of the probe fiber 31, the first fluctuation curve, which is the relationship between the position of the tip of the probe fiber 31 and the light intensity of leaked light, has a wide shape. Yes (solid line), full width at half maximum is about 71 μm. Although the light reception intensity is large, the full width at half maximum is wide and the optimum light reception position when receiving leaked light with a single mode fiber is unknown. Therefore, in the peak of the first curve, the central position of the coordinates at which the maximum intensity is half the value is set as the temporary optimum light receiving position (first position). In this graph, it is around 889.6 μm.

  Subsequently, the tip of the probe fiber 31 is moved to the temporary optimum light reception position. Next, the dedicated SMF 19 is divided between the DCF 11 and the light receiving device 15 to obtain a second fluctuation curve which is the relationship between the position of the tip of the probe fiber 31 and the light intensity of leaked light near the temporary optimum light receiving position. . The second variation curve is shown by a broken line. The dedicated SMF 19 is inserted and the light reception optimum position (true light reception optimum position: second position) when light is received by the single mode core of the probe fiber 31 is around 883 μm.

  The difference between the temporary light reception optimum position and the true light reception optimum position is only 6.6 μm, and both are close to each other. As described above, the rough alignment to receive leaked light is performed by the multimode core including the single mode core of the probe fiber 31 to set the temporary light reception optimum position, and then by the single mode core in the vicinity of the temporary light reception optimum position Fine alignment to receive leaked light can be performed in a short time and accurately.

(Embodiment 3)
In this embodiment, another method of the probe position alignment method of the optical fiber side input / output device 301 described in the second embodiment will be described. In the present embodiment, the control circuit 17 causes the aligning mechanism 12 to further move the one end of the probe fiber 31 to a third position separated from the second position by a predetermined distance.

  In the second embodiment, the position is optimized using the light emitted from the bending portion as an index. When the wavelength of the incident light is different from the wavelength of the received light, the maximum position of the light receiving coupling efficiency and the maximum position of the incident coupling efficiency are generally different because the refractive index of the optical material is different. is there. This relative positional relationship can be measured at the time of manufacture of the device or obtained by simulation. FIG. 12 is a simulation of a second variation curve in the case where the leaked light of wavelength 1310 nm and the leaked light of wavelength 1550 nm are received by the single mode core of the probe fiber 31. The difference between the second variation curve of wavelength 1310 nm and the second variation curve of wavelength 1550 nm is the relative positional relationship.

  Here, it is considered that the leaked light of the wavelength 1310 nm propagating in the main optical fiber 1 is received, and the light of the wavelength 1550 nm is incident on the main optical fiber 1. From FIG. 12, even if the probe fiber 31 is finely aligned by the probe position alignment method as in Embodiment 2 using leaked light having a wavelength of 1310 nm, the optimum position of the probe fiber 31 that causes light of a wavelength of 1550 nm to enter the main optical fiber 1 Are expected to be offset by 8 μm.

  Therefore, after the probe fiber 31 is aligned to the optimum position by the probe position alignment method as in Embodiment 2 using the received wavelength, the incidence coupling efficiency previously investigated at the desired wavelength becomes optimum. By shifting the probe fiber 31 to the position (third position), the incidence coupling efficiency can be maximized. By moving the probe fiber 31 to the position where the incidence coupling efficiency is maximum, the probe fiber 31 is separated from the optimum position of the light reception coupling efficiency by the single mode core, but the light reception is performed by the multimode core having a wide position tolerance. A value close to the optimum value is also obtained for the light receiving coupling efficiency.

(Embodiment 4)
13 to 15 are diagrams for explaining an optical fiber side input / output device 302 of this embodiment. The optical fiber side input / output device 302 is an optical fiber side input / output device that inputs / outputs light to / from the main optical fiber 1 in which the bending portion is formed via the bending portion,
A double-clad fiber 11 having a single mode core and a multimode core, one end of which is close to the bent portion, and incident light is incident on the bent portion from the single mode core of the cross section of the one end and leaks from the bent portion A probe fiber 31 for receiving leaked light by the single mode core and the multi mode core of the cross section of the one end;
An optical switch 21 for coupling the leaked light propagated by the probe fiber 31 to a dedicated double clad fiber 20 or a dedicated single mode fiber 19;
A light receiving device 15A for double clad fiber which receives the leaked light propagated by the dedicated double clad fiber 20 connected to the optical switch 21 and measures the light intensity of the leaked light;
A light receiving device 15B for single mode fiber which receives the leaked light propagated by the dedicated single mode fiber 19 connected to the optical switch 21 and measures the light intensity of the leaked light;
An alignment mechanism 12 for adjusting the position of the one end of the probe fiber 31;
A control circuit 17 for causing the alignment mechanism 12 to adjust the position of the one end of the probe fiber 31 based on the light intensity of the leaked light measured by the double clad fiber light receiving device 15A or the single mode fiber light receiving device 15B;
Equipped with
The optical fiber side input / output device 302 further includes a repeater amplifier 33 having a WDM coupler 34, a duplex SFP optical transceiver 35, a bi-directional SFP optical transceiver 36, an SMF 37, and a DCF 38. The probe fiber 31 and the alignment mechanism 12 are provided in the local light input / output unit 32. The optical switch 21, the light receiving devices (15 A, 15 B), and the control circuit 17 may be in the relay amplifier 33.

  The optical fiber side input / output device 301 of the first embodiment performs probe position alignment by inserting a dedicated SMF 19. The optical fiber side input / output device 302 can automate the assignment of the dedicated SMF 19 by introducing the optical switch 21 (see, for example, Non-Patent Document 5). The DCF 11 from the probe fiber 31 is connected to the optical switch 21. The optical switch 21 is connected to the WDM coupler 34, the light receiving device 15A for DCF, and the light receiving device 15B for SMF, and can be switched mutually. The light receiving device 15A for DCF and the light receiving device 15B for SMF are PDs with high sensitivity similar to the light receiving device 15 described in the first embodiment.

The following shows the procedure. The operation of the optical switch 21 may be performed by an instruction from the control circuit 17.
(Step 1: FIG. 13) The light switch 21 is operated to connect the light from the DCF 11 to the dedicated DCF 20, and the control circuit 17 is adjusted with the light intensity (first fluctuation curve) received by the light receiving device 15A for DCF as an index. Coarse alignment is performed with the heart mechanism 12. Specifically, the control circuit 17 estimates a peak center from the first variation curve, moves the probe fiber 31 to the position, and holds the probe fiber 31 at the position.

(Step 2: FIG. 14) The light switch 21 is operated to connect the light from the DCF 11 to the dedicated SMF 19, and the control circuit 17 is adjusted with the control circuit 17 using the light intensity (second variation curve) received by the SMF light receiving device 15B as an index. Fine-tune the mind mechanism 12 Specifically, the control circuit 17 detects the peak center from the second fluctuation curve, moves the probe fiber 31 to the position, and holds the probe fiber 31 at the position.

(Procedure 3: FIG. 15) While maintaining the optimum position of the probe fiber 31, the optical switch 21 is operated to connect the light from the DCF 11 to the WDM coupler 34 to start bi-directional communication. The signal flow of the two-way communication is the same as described in the first embodiment.

  As described above, by adjusting the position of the probe fiber 31 by the present probe position alignment method, bi-directional communication is possible in a state in which both the light incident on the main optical fiber 1 and the leaked light from the main optical fiber 1 have high coupling efficiency. become.

Embodiment 5
16 to 19 are diagrams for explaining the optical fiber side input / output device 303 of this embodiment. The optical fiber side input / output device 303 is an optical fiber side input / output device that inputs / outputs light to / from the main optical fiber 1 in which the bending portion is formed via the bending portion,
A double-clad fiber 11 having a single mode core and a multimode core, one end of which is close to the bent portion, and incident light is incident on the bent portion from the single mode core of the cross section of the one end and leaks from the bent portion A probe fiber 31 for receiving leaked light by the single mode core and the multi mode core of the cross section of the one end;
A dedicated single mode fiber 19 that can be connected to the other end of the probe fiber 31 and propagates the leaked light propagated in the single mode core of the probe fiber 31;
A connector 22 to which the other end of the probe fiber 31 or the other end of the dedicated single mode fiber 19 can be connected;
A duplex type optical transceiver 35 that receives the leaked light coupled to the connector 22 with a photodiode and outputs the light intensity of the leaked light;
An alignment mechanism 12 for adjusting the position of the one end of the probe fiber 31;
a control circuit 17 for causing the alignment mechanism 12 to adjust the position of the one end of the probe fiber 31 based on the light intensity of the leaked light output from the duplex optical transceiver 35;
Equipped with
The optical fiber side input / output device 303 further includes a repeater amplifier 33 having a WDM coupler 34, a bi-directional SFP optical transceiver 36, an SMF 37, and a DCF 38. The probe fiber 31 and the alignment mechanism 12 are provided in the local light input / output unit 32. The control circuit 17 may be in the relay amplifier 33.

  In the optical fiber side input / output device 301 of the first embodiment and the optical fiber side input / output device 302 of the fourth embodiment, light receiving devices are prepared. A light reception intensity output terminal may be added to the duplex SFP optical transceiver 35, and the light reception intensity of the communication light reception APD may be externally output to be used for probe position alignment. The optical fiber side input / output device 303 substitutes the photodiode in the duplex SFP optical transceiver 35 for the light receiving device by providing the duplex SFP optical transceiver 35 with the light receiving intensity output terminal.

The optical fiber side input / output device 303, like the optical fiber side input / output device 301 of the first embodiment, divides and connects the dedicated SFP 19 between the DCF 11 and the WDM coupler 34 only during fine alignment. The following shows the procedure.
(Procedure 1: FIG. 16) The DCF 11 is connected to the connector 22 and the light from the DCF 11 is connected to the duplex SFP optical transceiver 35 through the WDM coupler 34 and the DCF 38 (all path DCF). Rough adjustment is performed by the control circuit 17 and the alignment mechanism 12 using the light intensity (first variation curve) received by the photodiode of the duplex SFP optical transceiver 35 as an index. Specifically, the control circuit 17 estimates a peak center from the first variation curve, moves the probe fiber 31 to the position, and holds the probe fiber 31 at the position.

(Procedure 2: FIG. 17) A dedicated SMF 19 is inserted between the DCF 11 and the connector 22 and connected to the duplex SFP optical transceiver 35 through the dedicated SMF 19, the WDM coupler 34 and the DCF 38. Fine alignment is performed by the control circuit 17 and the alignment mechanism 12 using the light intensity (second variation curve) received by the photodiode of the duplex SFP optical transceiver 35 as an index. Specifically, the control circuit 17 detects the peak center from the second fluctuation curve, moves the probe fiber 31 to the position, and holds the probe fiber 31 at the position. The dedicated SMF 19 may be installed on the surface of the relay amplifier 33 in advance.

(Procedure 3: FIG. 18) While keeping the optimum position of the probe fiber 31 found in the procedure 2, remove the dedicated SMF 19 inserted.

(Step 4: FIG. 19) Reconnect DCF 11 to connector 22. The light from the DCF 11 is connected to the WDM coupler 34 to start bi-directional communication. The signal flow of the two-way communication is the same as described in the first embodiment.

  As described above, by adjusting the position of the probe fiber 31 by the present probe position alignment method, bi-directional communication is possible in a state in which both the light incident on the main optical fiber 1 and the leaked light from the main optical fiber 1 have high coupling efficiency. become.

Embodiment 6
FIGS. 20 to 22 are diagrams for explaining the optical fiber side input / output device 304 of this embodiment. The optical fiber side input / output device 304 is an optical fiber side input / output device that inputs / outputs light to / from the main optical fiber 1 in which the bending portion is formed via the bending portion,
A double-clad fiber 11 having a single mode core and a multimode core, one end of which is close to the bent portion, and incident light is incident on the bent portion from the single mode core of the cross section of the one end and leaks from the bent portion A probe fiber 31 for receiving leaked light by the single mode core and the multi mode core of the cross section of the one end;
An optical switch 23 for coupling the leaked light propagated by the probe fiber 31 to the relay path 25 of the double clad fiber or the dedicated single mode fiber 19;
A duplex type optical transceiver 35 which receives the leaked light propagated in the double clad fiber relay path 25 or the dedicated single mode fiber 19 by a photodiode and outputs the light intensity of the leaked light;
An alignment mechanism 12 for adjusting the position of the one end of the probe fiber 31;
a control circuit 17 for causing the alignment mechanism 12 to adjust the position of the one end of the probe fiber 31 based on the light intensity of the leaked light output from the duplex optical transceiver 35;
Equipped with
The optical fiber side input / output device 304 further includes a WDM coupler 34, an optical switch 24, a bi-directional SFP optical transceiver 36, an SMF 37, and a relay amplifier 33 having a DCF 38. The optical switch 24 couples either the light from the dedicated SMF 19 or the light from the WDM coupler 34 to the DCF 38. The probe fiber 31 and the alignment mechanism 12 are provided in the local light input / output unit 32. The optical switch 23 and the control circuit 17 may be in the relay amplifier 33.

  The optical fiber side input / output device 304 uses a duplex SFP optical transceiver 35 having a light reception intensity output terminal similarly to the optical fiber side input / output device 303 of the fifth embodiment, and only when the probe fiber 31 is finely aligned The light passing through the dedicated SMF 19 is coupled to the duplex SFP optical transceiver 35. In detail, two optical switches are set before and after the WDM coupler 34 (reference numerals 23 and 24), and at the time of fine alignment, leaked light is made to pass through the dedicated SMF 19 instead of the WDM coupler 34.

The following shows the procedure. The operations of the optical switches 23 and 24 may be performed by an instruction from the control circuit 17.
(Procedure 1: FIG. 20) The optical switch 23 is operated to make the light from the DCF 11 enter the duplex SFP optical transceiver 35 through the path of the relay path 25, the WDM coupler 34, the optical switch 24 and the DCF 38 (full path DCF). Rough adjustment is performed by the control circuit 17 and the alignment mechanism 12 using the light intensity (first variation curve) received by the photodiode of the duplex SFP optical transceiver 35 as an index. Specifically, the control circuit 17 estimates a peak center from the first variation curve, moves the probe fiber 31 to the position, and holds the probe fiber 31 at the position.

(Procedure 2: FIG. 21) The light switch 23 is operated to connect the light from the DCF 11 to the dedicated SMF 19 and to the duplex SFP optical transceiver 35 through the path of the dedicated SMF 19, the light switch 24 and the DCF 38. Fine alignment is performed by the control circuit 17 and the alignment mechanism 12 using the light intensity (second variation curve) received by the photodiode of the duplex SFP optical transceiver 35 as an index. Specifically, the control circuit 17 detects the peak center from the second fluctuation curve, moves the probe fiber 31 to the position, and holds the probe fiber 31 at the position.

(Step 3: FIG. 22) While maintaining the optimum position of the probe fiber 31, operate the optical switch 23 to operate the light from the DCF 11 in the path of the relay path 25, the WDM coupler 34, the optical switch 24, and the DCF 38 The beam is incident on 35 to start two-way communication. The signal flow of the two-way communication is the same as described in the first embodiment.

  As described above, by adjusting the position of the probe fiber 31 by the present probe position alignment method, bi-directional communication is possible in a state in which both the light incident on the main optical fiber 1 and the leaked light from the main optical fiber 1 have high coupling efficiency. become.

Seventh Embodiment
23 to 25 are diagrams for explaining an optical fiber side input / output device 305 of the present embodiment. The optical fiber side input / output device 305 is an optical fiber side input / output device that inputs / outputs light to / from the main optical fiber 1 in which the bending portion is formed via the bending portion,
A double-clad fiber 11 having a single mode core and a multimode core, one end of which is close to the bent portion, and incident light is incident on the bent portion from the single mode core of the cross section of the one end and leaks from the bent portion A probe fiber 31 for receiving leaked light by the single mode core and the multi mode core of the cross section of the one end;
An optical switch 26 for coupling the leaked light propagated by the probe fiber 31 to the relay path 25 of the double clad fiber or the dedicated single mode fiber 19;
A duplex type optical transceiver 35 which receives the leaked light propagated in the relay path 25 of the double clad fiber by a photodiode and outputs the light intensity of the leaked light;
A light receiving device 15 which receives the leaked light propagated by the dedicated single mode fiber 19 and measures the light intensity of the leaked light;
An alignment mechanism 12 for adjusting the position of the one end of the probe fiber 31;
a control circuit 17 for causing the alignment mechanism 12 to adjust the position of the one end of the probe fiber 31 based on the light intensity of the leaked light output from the duplex type optical transceiver 35 or the light intensity of the leaked light measured by the light receiving device 15;
Equipped with
The optical fiber side input / output device 305 further comprises a repeater amplifier 33 having a WDM coupler 34, a bi-directional SFP optical transceiver 36, an SMF 37, and a DCF 38. The probe fiber 31 and the alignment mechanism 12 are provided in the local light input / output unit 32. The optical switch 26, the relay path 25, the light receiving device 15, and the control circuit 17 may be in the relay amplifier 33.

  In the optical fiber side input / output device 304 of the sixth embodiment, rough alignment and fine alignment are performed using the signal from the light receiving intensity output terminal of the duplex SFP optical transceiver 35 as an index. Since the light passing through the dedicated SMF 19 at the time of fine alignment is weak, the optical fiber side input / output device 305 uses a high sensitivity light receiving device 15 (for example, a high sensitivity large aperture photodiode) only at the time of fine alignment.

The following shows the procedure. The operation of the optical switch 26 may be performed by an instruction from the control circuit 17.
(Procedure 1: FIG. 23) The optical switch 26 is operated to connect the light from the DCF 11 to the duplex SFP optical transceiver 35 through the relay path 25, the WDM coupler, and the DCF 38 (all path DCF). Rough adjustment is performed by the control circuit 17 and the alignment mechanism 12 using the light intensity (first variation curve) received by the photodiode of the duplex SFP optical transceiver 35 as an index. Specifically, the control circuit 17 estimates a peak center from the first variation curve, moves the probe fiber 31 to the position, and holds the probe fiber 31 at the position.

(Procedure 2: FIG. 24) The light switch 26 is operated to connect the light from the DCF 11 to the dedicated SMF 19, and the control circuit 17 and the alignment mechanism are used with the light intensity (second variation curve) received by the light receiving device 15 as an index. Fine-tune at 12 Specifically, the control circuit 17 detects the peak center from the second fluctuation curve, moves the probe fiber 31 to the position, and holds the probe fiber 31 at the position.

(Procedure 3: FIG. 25) While maintaining the optimum position of the probe fiber 31, the light switch 21 is operated to connect the light from the DCF 11 to the WDM coupler 34 to start bi-directional communication. The signal flow of the two-way communication is the same as described in the first embodiment.

  As described above, by adjusting the position of the probe fiber 31 by the present probe position alignment method, bi-directional communication is possible in a state in which both the light incident on the main optical fiber 1 and the leaked light from the main optical fiber 1 have high coupling efficiency. become.

(Other embodiments)
In the first to seventh embodiments, the case where the main optical fiber has one core has been described for simplicity. However, when the main optical fiber is a tape fiber having a plurality of optical fibers (FIG. 4), Use a fiber input / output device.

  Further, the bent portion of the main optical fiber can be formed, for example, by a jig as described in Non-Patent Document 4.

1: Main optical fiber 11: DCF
12: alignment mechanism 14: GRIN lens 15: light receiving device 15A: light receiving device 15B for DCF: light receiving device 17 for SMF: control circuit 19: dedicated SMF
20: Dedicated DCF
21, 23, 24, 26: Optical switch 22: Connector 25: Relay path 31: Probe fiber 32: Local light input / output unit 33: Relay amplifier 34: WDM coupler 35: duplex SFP optical transceiver 36: bi-directional SFP optical transceiver 37: SMF (single mode fiber)
38: DCF (double clad fiber)
300 to 305: Fiber side input / output device

Claims (8)

An optical fiber side input / output device for inputting / outputting light to / from a main optical fiber in which a bending portion is formed via the bending portion,
A double clad fiber having a single mode core and a multi mode core, one end of which is close to the bend, and the incident light is made incident from the single mode core of the cross section of the one end to the bend and leaked from the bend A probe fiber for receiving light by a single mode core and a multi mode core of the cross section of the one end;
A dedicated single mode fiber that can be connected to the other end of the probe fiber and propagates the leaked light propagated in the single mode core of the probe fiber;
A light receiving device for receiving the leaked light received by the probe fiber from the probe fiber directly or through the dedicated single mode fiber, and measuring the light intensity of the leaked light;
An alignment mechanism for adjusting the position of the one end of the probe fiber;
A control circuit that causes the aligning mechanism to adjust the position of the one end of the probe fiber based on the light intensity of the leaked light measured by the light receiving device;
An optical fiber side input / output device comprising: An optical fiber side input / output device for inputting / outputting light to / from a main optical fiber in which a bending portion is formed via the bending portion,
A double clad fiber having a single mode core and a multi mode core, one end of which is close to the bend, and the incident light is made incident from the single mode core of the cross section of the one end to the bend and leaked from the bend A probe fiber for receiving light by a single mode core and a multi mode core of the cross section of the one end;
An optical switch for coupling the leaked light propagated by the probe fiber to a dedicated double clad fiber or a dedicated single mode fiber;
A light receiving device for double clad fiber which receives the leaked light propagated by the dedicated double clad fiber connected to the optical switch and measures the light intensity of the leaked light;
A light receiving device for a single mode fiber that receives the leaked light propagated by the dedicated single mode fiber connected to the optical switch and measures the light intensity of the leaked light;
An alignment mechanism for adjusting the position of the one end of the probe fiber;
A control circuit that causes the alignment mechanism to adjust the position of the one end of the probe fiber based on the light intensity of the leaked light measured by the double clad fiber light receiving device or the single mode fiber light receiving device;
An optical fiber side input / output device comprising: An optical fiber side input / output device for inputting / outputting light to / from a main optical fiber in which a bending portion is formed via the bending portion,
A double clad fiber having a single mode core and a multi mode core, one end of which is close to the bend, and the incident light is made incident from the single mode core of the cross section of the one end to the bend and leaked from the bend A probe fiber for receiving light by a single mode core and a multi mode core of the cross section of the one end;
A dedicated single mode fiber which can be connected at one end to the other end of the probe fiber and which propagates the leaked light propagated in a single mode core of the probe fiber;
A connector capable of connecting the other end of the probe fiber or the other end of the dedicated single mode fiber;
A duplex type optical transceiver that receives the leaked light coupled to the connector by a photodiode and outputs the light intensity of the leaked light;
An alignment mechanism for adjusting the position of the one end of the probe fiber;
A control circuit that causes the alignment mechanism to adjust the position of the one end of the probe fiber based on the light intensity of the leaked light output from the duplex optical transceiver;
An optical fiber side input / output device comprising: An optical fiber side input / output device for inputting / outputting light to / from a main optical fiber in which a bending portion is formed via the bending portion,
A double clad fiber having a single mode core and a multi mode core, one end of which is close to the bend, and the incident light is made incident from the single mode core of the cross section of the one end to the bend and leaked from the bend A probe fiber for receiving light by a single mode core and a multi mode core of the cross section of the one end;
An optical switch for coupling the leaked light propagated by the probe fiber to a relay path of a double clad fiber or a dedicated single mode fiber;
A duplex type optical transceiver which receives the leaked light propagated in the relay path of the double clad fiber or the dedicated single mode fiber by a photodiode and outputs the light intensity of the leaked light;
An alignment mechanism for adjusting the position of the one end of the probe fiber;
A control circuit that causes the alignment mechanism to adjust the position of the one end of the probe fiber based on the light intensity of the leaked light output from the duplex optical transceiver;
An optical fiber side input / output device comprising: An optical fiber side input / output device for inputting / outputting light to / from a main optical fiber in which a bending portion is formed via the bending portion,
A double clad fiber having a single mode core and a multi mode core, one end of which is close to the bend, and the incident light is made incident from the single mode core of the cross section of the one end to the bend and leaked from the bend A probe fiber for receiving light by a single mode core and a multi mode core of the cross section of the one end;
An optical switch for coupling the leaked light propagated by the probe fiber to a relay path of a double clad fiber or a dedicated single mode fiber;
A duplex type optical transceiver that receives the leaked light propagated in the relay path of the double clad fiber with a photodiode and outputs the light intensity of the leaked light;
A light receiving device which receives the leaked light propagated by the dedicated single mode fiber and measures the light intensity of the leaked light;
An alignment mechanism for adjusting the position of the one end of the probe fiber;
A control circuit that causes the aligning mechanism to adjust the position of the one end of the probe fiber based on the light intensity of the leaked light output from the duplex optical transceiver or the light intensity of the leaked light measured by the light receiving device;
An optical fiber side input / output device comprising: The control circuit
The position of the one end of the probe fiber is moved with respect to the alignment mechanism, the light intensity of the leaked light not measured through the dedicated single mode fiber is measured, and the leaked light with respect to the position of the one end of the probe fiber Acquire the first variation curve of the light intensity of
Moving the one end of the probe fiber to a first position centered on the full width at half maximum of the first variation curve with respect to the alignment mechanism;
The position of the one end of the probe fiber is moved in the vicinity of the first position with respect to the alignment mechanism, and the light intensity of the leaked light through the dedicated single mode fiber is measured to obtain the probe fiber Acquiring a second variation curve of the light intensity of the leaked light with respect to the position of one end,
The optical fiber side entrance according to any one of claims 1 to 5, wherein the one end of the probe fiber is moved to a second position where the second fluctuation curve peaks with respect to the alignment mechanism. Output device. The control circuit
The optical fiber lateral input / output device according to claim 6, wherein the one end of the probe fiber is further moved to a third position spaced apart from the second position by a predetermined length with respect to the alignment mechanism. A probe position alignment method for an optical fiber side input / output device according to claim 1, comprising:
The first variation of the light intensity of the leaked light relative to the position of the one end of the probe fiber by moving the position of the one end of the probe fiber and measuring the light intensity of the leaked light not passing through the dedicated single mode fiber A rough alignment step of acquiring a curve and moving the one end of the probe fiber to a first position at the center of the full width at half maximum of the first variation curve;
The position of the one end of the probe fiber is moved in the vicinity of the first position, the light intensity of the leaked light through the dedicated single mode fiber is measured, and the leaked light relative to the position of the one end of the probe fiber A fine adjustment step of acquiring a second variation curve of light intensity and moving the one end of the probe fiber to a second position at which the second variation curve peaks with respect to the alignment mechanism;
A probe position centering method characterized by performing.

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